1. Field of the Invention
The present invention relates generally to a battery powered hand-held communication system, such as a cordless phone system and a mobile phone system, and in particular to an enhanced power saving method for operating the battery powered communication system in an enhanced power saving standby mode in which the receiver of the communication system changes the scan rate as a function of the standby time and enters a sleep mode if no incoming signal is received or no outgoing signal is transmitted in order to save on power consumed by the receiver.
The invention is also directed to an enhanced power saving cordless communication system which comprises a controller changing the scan rate of the receiver as a function of the standby time in order to minimize the power consumed in the standby interval.
2. Brief Discussion of Prior Art
Prolonging the standby time of a battery powered cordless communication system, especially a hand-held cordless communication system, is a challenge to the communication industry. A hand-held cordless communication system includes, in general, a receiver for incoming signals and a transmitter for outgoing signals. For a conventional hand-held cordless communication system, its operation is divided as a talk mode TM in which both the receiver and the transmitter are active and a standby mode in which the transmitter is inactive with the power supplied thereto completely cut off while the receiver remains in an active mode so as to scan for incoming signals from the surrounding air.
For a conventional cordless phone system, the power consumptions of the transmitter and the receiver thereof are respectively illustrated in FIGS. 1 and 2 of the attached drawings. As illustrated in FIG. 1, the transmitter consumes no power at all in the standby mode. However, as shown in FIG. 2, the receiver takes the same amount of power in both the talk mode and the standby mode since it maintains itself in an active mode. As a result, the overall system power consumption of the conventional hand-held cordless communication system is generally the sum of FIGS. 1 and 2, which sum is illustrated in FIG. 3.
An interpretation of FIGS. 1, 2 and 3 indicates that in the talk mode, both the transmitter and the receiver consume power, while in the standby mode, only the receiver takes power to maintain the active mode. Since the receiver has to be maintained in the active mode, power supplied thereto cannot be cut off. Such a system requires a substantial power consumption to maintain the receiver in the active mode all of the time. Since the incoming signals are coming in a random fashion, maintaining the receiver in the active mode represents quite a loss from the point of view of power-saving.
Another type of the hand-held cordless communication system uses a software algorithm to control the power supply. In a communication system of this kind, the power supply to the transmitter is the same as previously discussed, i.e., power is only consumed in the talk mode. However, the power supply to the receiver is made intermittent, as shown in FIG. 4.
In the communication system illustrated in FIG. 4, the standby mode contains a scanning mode when the receiver is active to scan for incoming signals and a sleep mode when the receiver is deactivated and the power supplied thereto is completely cut off. In the scanning mode, the receiver is powered to scan for incoming signals from the surrounding air within a predetermined period. Once no incoming signal is detected in this predetermined period, the power is shut down and the receiver enters the sleep mode. The receiver will sleep for a given fixed sleeping period and is then activated to enter the scanning mode again. This procedure will be continuously repeated unless a call is made. Apparently, the power is completely cut off to both the receiver and the transmitter in the sleep mode. Normally, the scanning period, namely the predetermined period within which the receiver is activated to scan for incoming signals, is approximately 1/5 or 1/10 of the sleeping period of the sleep mode which, as can be understood, is the time interval between two successive scan modes.
In the above-mentioned conventional power saving communication system, the scan rate, which is used herein to denote the number of the scan modes occurring in a given length of time in the standby mode, is fixed. This kind of system does provide a significant reduction in the overall power consumption, as illustrated in FIG. 5.
The conventional power saving communication system, although effective in cutting down on power consumption, still wastes a great deal of power in the standby mode, especially during the night when the communication system is generally not used for a very long while.
Due to the development of the even smaller and lighter battery powered hand-held communication system, the power consumption will be subject to a more severe restriction. Thus, a more effective algorithm is desired to handle these more severe requirement of power consumption for the battery powered hand-held cordless communication systems.
In the current cordless phone market, one of the most advanced systems is the so-called multiple channel access (MCA) auto-scan cordless phone which includes a base powered by an external power source and a battery powered handset with a multiplicity of electromagnetic link channels connecting these two parts. The MCA auto-scan cordless phone, as implied by the name, scans all of the multiple link channels to seek and establish the best communication between the base and the handset.
To meet the requirement of the end users, the MCA auto-scan cordless phone system has to provide a fast but power efficient link between the base and the handset to meet PTT regulations and to prolong the overall operation time that the battery in the handset can provide. To be fast, a high data rate of communication should be established between the base and the handset and, as known to the art, PTT regulations should be followed regarding the data rate. The requirement of high data rate can be solved by using high speed modulating/demodulating techniques, such as 1200 or 2400 bps (baud per second) modem chips. An example of a known circuit, which adopts the high speed modulating/demodulating technique, is illustrated in FIG. 6, which arrangement was proposed by the SONY company. The circuit in FIG. 6 includes a modulating/demodulating device with the speed of 1200 bps 61 to process the signals communicated between the base and the handset, e.g., an MSK modem. The signals after modulation/demodulation are transmitted by a transmitter 63 via a audio control circuit 62. In standby mode, the receiver 64 scans the signals of the multiple channels with a fixed scanning rate. Further shown are a duplexer 65, a synthesizer 66, and an antenna 67, voice V.sub.o and data D.sub.a signals being present.
Although the high speed modulating/demodulating technique provides a high data rate, the power saving problem is still not overcome. The power saving problem is very severe for the MCA auto-scan cordless phone because (1) it is powered by a limited battery power source and (2) it takes a great deal of power to scan all of the channels continuously. The conventional power saving algorithm, as discussed above, has been widely used to resolve the power saving problem so as to prolong the overall standby time provided by a battery set. As discussed previously, such a conventional power saving algorithm is not very effective and thus it is desirable to have a more effectual power saving method to further prolong the standby time that a battery can provide.